Preliminary Study Of Remediation Of Heavy Metals By Extracellular Polymeric Substances Excreted From Aspergillus Tubingensis F12

The heavy metal polluted soil in our country has made simple and cheap passivation repair technology become a hot spot.At the same time,soil leaching technology is used to control the spread of heavy metals in sudden pollution.As a heavy metal repair agent,microbe cells can not contact with heavy metal ions in the soil,and it is difficult to separate after the reaction,which leads to the limitation of practical application.Microbial extracellular polymeric substances(EPS)have been proved to be the main substances for microbial adsorption of heavy metals.This paper attempts to investigate the potential application of EPS as a remediation agent in heavy metal remediation by soil leaching and passivation technology.There are few reports on the adsorption of heavy metals by Aspergillus flavus.A strain of Aspergillus sp.F12 was isolated from the local area,and the adsorption capacity of hypha and EPS was verified by liquid phase reaction.The study found that the adsorption of heavy metals by Aspergillus sp.F12 has a good broad-spectrum.The effect of adsorption is:lead(52.04 mg/g)>chromium(37.18 mg/g)>zinc(18.40 mg/g)>nickel(?)(6.66 mg/g)>copper(5.10 mg/g)>cadmium(3.01 mg/g).In the multi metal system,the removal rates of chromium,lead(?)and zinc(?)were reduced by 39.99%,12.69%and 51%respectively.The study of the multi metal system was more instructive to the practical application.EPS is the main substance to adsorb heavy metals by Aspergillus sp.F12.Under the condition of heavy metal concentration of 50 mg/L,the adsorption capacity of EPS of the less bacteria ball 10%is more than 30%of the bacterial silk ball.Aspergillus tubingensis F12 EPS has potential applications in soil heavy metal remediation.Leaching method can quickly clean heavy metals in contaminated soil.In this paper,the response surface method was used to analyze the effects of four factors,velocity,pH,EPS concentration and ionic strength,on cadmium(?),chromium(?),nickel(?),nickel(?),lead(?)and zinc(?)in the mixed contaminated soil which were simultaneously eluted from the EPS of strain F12.It was found that the EPS restorant retained the broad-spectrum of Aspergillus tubingensis.The removal efficiency of cadmium(?),chromium,copper(?),nickel(?),lead(?),lead(?)and zinc(?)were 1.21 mg/g,0.25 mg/g,0.43 mg/g,0.45 mg/g,8.66 mg/g and 2.68 mg/g,respectively,which were equivalent to the artificial chelating agent.The influence of pH and EPS concentration on the elution amount is more significant,and there is synergy between the two factors.The mechanism of elution was preliminarily studied by Fourier transform infrared spectroscopy,X ray photoelectron spectroscopy,scanning electron microscopy and energy dispersive spectrometry.The results showed that adsorption,redox and ion exchange simultaneously existed dning the elution process.Reducing effective metals absorbed by plants is also one of the strategies to deal with heavy metals endangering human beings.In this paper,we found that EPS,derived from strain F12,has a synergistic effect on the available heavy metal process of phosphate passivation.The effects of four factors,such as EPS concentration,pH value,phosphorus concentration and agents' volume,on the simultaneous passivation of cadmium(?),copper(?),nickel(?),lead(?)and zinc(?)in soil were analyzed by response surface method.The results showed that this method is simple,without artificial mixing and incubation.Under the laboratory scale,the technological process takes only 5 days,and the effective state lead(?)passivation rate is over 80%.Environmental friendliness is the advantage of microbiological restoratives.In order to confirm the environmental friendliness of EPS,the changes of soil physical and chemical properties and the evolution of indigenous microbial communities before and after EPS leaching have been measured.The results showed that EPS had no significant effect on soil pH,conductivity and organic carbon,and the evolution of soil microbial community was in a controllable range.By genomics analysis,it is believed that the EPS added into the soil is identified by microbes as nutrients,and indigenous microorganisms do not produce a defense mechanism of stress,which is consistent with the biological sources of EPS.